Ski slopes having a surface coating comprising a particulate resinous composition



1966 D. D. APPLEGATH ETAL 3,291,486

SKI SLOPES HAVING A SURFACE COATING COMPRISING A PARTICULATE RESINOUS COMPOSITION Filed June 26, 1962 y b ai @Qibfirwl I I INVENTORS.

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Doug/06 Q fipp/egal /z United States Patent SKI SLOPES HAVING A SURFACE COATING CGM- gll tlgglgG A PARTlCULATE RESINOUS COMPO- Douglas D. Applegath and Robert E. Erickson, Midland,

Mich, assignors to The Dow Chemical Company, Midland, Mich, a corporation of Delaware Filed June 26, 1962, Ser. No. 205,352 7 Claims. (Cl. 27256.5)

This invention relates to a ski slope. It more particularly relates to an improved surface coating for use on such slopes.

The sport of skiing has become very popular in recent years, but unfortunately, enjoyment of this sport has generally been confined to a relatively short season. With the shortness of the season now available to ski enthusiasts, it is generally not possible to keep in physical training since the muscles used in skiing become soft in the interval between seasons. There also results a considerable loss of experience in the skiing skill. A number of attempts have been made to prepare a suitable synthetic slope for skiing. Among these there are included slopes utilizing brushes aligned with their bristles uppermost to provide a resilient surface. Small glass spheres embedtied in a waxy matrix, resilient mats having a plurality of generally dome-like protrusions afiixed to the surface thereof and the like. Such devices have proved relatively expensive and in general have not provided an economic practical substitute for snow. Numerous materials such as borax, sugar, salt, soap powder, and other substances have been used in connection with a carpet to similate a ski surface. Such a surface, after use, becomes compacted and is more like ice than snow and usually does not permit much speed of travel. A major objection to such forms of substitute for snow is that the moment that they are exposed to rain or moisture as would be the case in outdoor use, many of the materials are dissolved. Lubricants such as soaps, greases, oils, etc. have the obvious objection of soiling the clothes of the skiier and being generally messy. A further objection is that most of the ingredients do not have a suflieiently low coefficient of friction. A successful artificial ski surface must be capable of outdoor use where it is subjected to changes of heat, cold and moisture. It is essential that such changes do not adversely affect the skiing qualities such as speed, control, and the like. Where the ski surface is to be subjected to considerable use the ski surface must be maintained as slippery as possible, that is, to have a relatively low coeflicient of friction so that skiing speed is maintained and the useful life of material is as long as possible. Further, such a ski slope should have the property of being readily installed, repaired, and preferably have the skiing characteristics generally associated with corn snow. The term corn snow generally as used herein refers to the coarse granular snow composed of ice crystals having generally the size of corn kernels.

It is an object of this invention to provide an improved synthetic ski slope.

It is a further object of this invention to provide an improved synthetic ski slope having generally the characteristics of snow.

It is a further object of this invention to provide an improved ski slope having a surface of loose particulate material.

It is a further object of this invention to provide an improved ski slope utilizing a thermoplastic resinous composition.

These benefits and other advantages in accordance with the invention are achieved by providing a particulate coating on a slope for skiing, said particulate coating comprising a plurality of particles of irregular shape similar ice to crushed stone and glacial gravel, said particles passing through a one inch mesh and being retained on a inch mesh, each of said particles having a specific gravity of at least 0.9.

Further features and advantages of the invention will become more apparent when the following specification is taken in connection with the drawing wherein:

FIGURE 1 illustrates a ski slope in accordance with the invention on a hill;

FIGURE 2 illustrates a view of a plurality of particles in accordance with the invention.

in FIGURE 1 there is illustrated a hill generally designated by the reference numeral 1%. The bill lit is provided with a ramp 13, a slope 14, and a stopping area 15. The upwardly facing surface of the ramp 13, slope 14 and the stopping area 15 is covered with particles 18 of a thermoplastic resinous material depicted in FIGURE 2 to a depth of about 3 inches.

In the preparation of a ski slope in accordance with the invention generally the thermoplastic resinous particles utilized for surfacing such a slope are readily prepared using olefin polymers such as polyethylene, polypropylene and resinous copolymers thereof and like thermoplastic materials. Generally an advantageous method for the preparation of such particles comprises heating the thermoplastic resinous material to a temperature sufficiently high to render it fluid and subsequently admixing a suitable inert filler therewith cooling the resultant mixture to form one or more solid bodies substantially larger than the desired particles. Subsequently the solid bodies are then formed by crushing with a suitable mill, hammer, or the like to form particles of the desired dimension. Beneficially other substances such as waxes, oils and the like are readily incorporated in the composition during the melting of the polymer and addition of the P rticulate filler.

Usually, suitable thermoplastic resinous compositions are prepared utilizing from 10 to about 90 percent by weight of the total composition of the thermoplastic resinous polymer. Advantageously, however, usually from about 10 to about 70 percent of the total weight of the composition of polymeric resinous material is employed. In many instances in order to improve the lubricity of the composition a wax is employed. Such a wax may be utilized at levels up to about 80 percent by weight of the total composition and advantageously up to about 20 percent by weight of the total composition. Further reduction of the frictional resistance of the composition is obtained by utilizing up to about 20 percent by weight of the total composition of an oil such as a mineral oil and advantageously up to about 10 percent of the total weight of the composition.

A wide variety of fillers may be utilized, such as clay, calcium carbonate and like substances. Preferably, such fillers are white or at least light in color. Such light color fillers impart an appearance to the finally fabricated slope that is generally similar to that of natural snow. A particularly beneficial and advantageous filler is the mineral barytes (barium sulphate). Barytes has the particular advantage of generally occurring as a white material which on grinding and subsequent incorporation into a thermoplastic resinous material imparts a white appearance thereto and provides the added advantage of increasing the specific gravity of the resultant composition. The increased density of the composition is particularly advantageous where such skiing slopes are utilized in areas subjected to wind. The high density particles made utilizing barytes have much less tendency to be dislodged during wind storms and during skiing. Generally the quantity of filler which may be incorporated into the polymer varies from about 10 to about percent of the total weight of the composition and ada vantageously is maintained within the range of about 30 percent to about 70 percent of the total weight of the composition. At filler levels below about 10 percent insufficient material is incorporated within the polymer to provide adequate coloring for ski slope applications and there is usually insulficient inorganic material present to provide protection for the plastic matrix from ultraviolet rays of the sun and eventual decomposition of the matrix occurs. If the filler level exceeds about 75 percent of the total weight of the composition generally the physical strength of the particle becomes low and a coeflicient of friction increases. The maximum quantity of filler which may be incorporated into a polymer will vary depending on the particular particle size, shape and density of the filler. Thus, materials having a relatively high density and small surface can be incorporated into the polymeric compositions at higher levels than would be relatively low density high surface fillers such as diatomaceous earth and the like. For economic as well as practical service reasons, general ly it is beneficial to incorporate as much inorganic filler in the composition as possible and still retain the desired low frictional characteristics which permit satisfactory skiing.

To determine if a suitable proportion of filler has been incorporated in a particular formulation, it is desirable to determine an arbitrary value which is indicative of the coefficient of friction between the particulate material and the bearing surfaces of the skiis. A simple test of the coefficient of friction of a molded or otherwise regularly formed body against a surface was not believed to be representative of the results achieved by a particulate composition in place on a ski slope. A measurement related to the coefiicient of friction is found to correlate well with skiing properties of the particulate composition is made in the following manner: the plastic composition to be tested is prepared and poured into a mold to provide a test specimen measuring 2.8 by by 0.5 centimeters. One of the 2.8 by 5 centimeter faces is arbitrarily designated as the bottom face and is molded or is formed to be smooth and flat. The bottom face of the test specimen is then abraded by means of a silicon carbide water-proof sanding paper of 400 grit. A suitable paper may be obtained from the Bohr-Manning Company, Troy, New York, under the trade name of Tuf-Back. The surface is prepared by stroking the bottom face across the abrasive paper in a direction parallel to the long dimension of the test piece until a uniformly abraded surface is attained. The standard test surface is prepared by similarly treating a fiat sheet of chromium plated steel such as is commercially available as ferrotype tins abraded with the abrasive paper by moving the paper parallel to one edge of the sheet to provide a plurality of generally longitudinal scratches or grooves similar in roughness to the bottom side. ,of the test specimen. The abraded bottom surface of the test specimen is then placed on the abraded chromium plate in such a manner that the prepared surfaces are adjacent and that the scored grooves are in generally parallel relationship. The test surfaces are maintained in a horizontal position. A fixed load is then applied to the top of the test specimen to provide a total weight of 4.2 pounds. The weight of 4.2 pounds represents a pressure of 2 pounds per square inch of bearing surface. The test is carried out at a temperature of 75 Fahrenheit. The test sample is then drawn across the chromium surface to the plate in a direction parallel to the direction of abrasion by means of a spring loaded scale. The force required to slide the test specimen in pounds is then recorded.

Compositions which when evaluated in this manner and require a force of 2 pounds or less to draw the test specimen across the chromium plated surface are found to be satisfactory for skiing. Generally the preferred range is from about 1 to 1.5 pounds for most slopes; however,

in stopping areas, compositions requiring a force greater than 2 pounds are optionally utilized. The compositions requiring a force between about 1.5 pounds and about 2 pounds beneficially are utilized on steeper slopes to prevent excessive and dangerous rates of travel for the skiiers.

The following examples serve to illustrate the invention but are not to be considered limiting thereto.

Example I One hundred parts of linear polyethylene having a melt index of 2.77 is heated to a temperature sufiiciently high to render it fluid. To the molten polyethylene is added 75 parts of a paraflin wax which has a melting range of 143 to 150 Fahrenheit, 15 parts of mineral oil are incorporated in the parafiin wax polyethylene mixture, and subsequently 310 parts of the fine ground barytes are slowly stirred into the mixture until a uniform composition is obtained. The hot mixture is poured into a generally rectangular mold and cooled to about 75 Fahrenheit. A test specimen is prepared in the hereinbefore described manner and the force required to move the test specimen across the chromium plate is found to be 1.1 pounds. The hardened plastic composition is fractured into a plurality of irregular shaped particles and those passing a one inch mesh and retaned on a inch mesh are spread on a slope to a depth of about 3 inches and are found to be eminently satisfactory for skiing. Little or no tendency of the particles on the resultant ski slope to move with the wind or be affected by weather is observed.

Example II In a manner similar to Example I a composition is prepared employing: 100 parts of high pressure low density polyethylene having a melt index of 28 and a density of 0.915, 75 parts of a paraffin wax having a melting range of 135 to 137 Fahrenheit, 1.5 parts of mineral oil and 300 parts of fine ground barytes. Commensurate beneficial skiing properties are observed and the force required to maintain the test specimen in motion is 1.5 pounds.

Example III In a manner similar to Example I a composition is employed utilizing 100 parts of a high pressure polyethylene having a melt index of 20 and a density of 0.915, 50 parts of ethylene-ethyl acrylate copolymer containing about parts of ethylene and 20 parts of ethyl acrylate copolymerized in the polymer molecule, the melt index of the copolymer is 18 and its density 0.928. One hundred and fifty parts of paraffin wax having a melt range of 135 to 137 Fahrenheit, 25 parts of mineral oil and 508 parts of fine ground barytes are also included The resultant product is crushed and screened and applied to a slope, and found very satisfactory. It is found to be slightly slower skiing than the products of Examples I and II, and on testing in the hereinbefore mentioned manner a force of 1.8 pounds is required.

Example IV In a manner similar to Example I, a composition was prepared employing parts of polypropylene, 75 parts of paraffin wax having a melting index range of to 137 Fahrenheit, 15 parts of mineral oil and 310 parts of fine ground barytes. The mixture is blended at a temperature of from about 350 to about 400 Fahrenheit. Subsequent evaluation on a ski slope indicates that satisfactory results are obtained.

Particulate thermoplastic compositions which exhibit the characteristics of requiring a force of about 2 pounds or less to draw a test sample across a sheet in the manner hereinbefore described are found to be eminently satisfactory for skiing purposes. Such formulations are readily prepared from such polymers as polyvinyl chloride, polyamide condensation polymers, polyalkenyl aromatic resinous materials such as polystyrene, cellulosic materials such as cellulose acetate, ethyl cellulose, cellulose butyrate and the like.

In the installation of ski slopes in accordance with the invention generally if the soil is sandy or soft clay, it is advisable to first provide a gravel layer over the ground to provide support for the plastic particles and prevent their loss into the ground when the ground is wet or otherwise softened. The gravel layer is subsequently covered with about 2 to 4 inches of the desired plastic particulate composition.

As is apparent from the foregoing specification, the manufacture of the present invention is susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. For this reason, it is to be fully understood that all of the foregoing is intended to be merely illustrative and is not to be construed or interpreted as being restrictuve or otherwise limiting of the present invention, excepting as it is set forth and defined in the hereto appended claims.

What is claimed is:

1. A ski slope having a particulate coating on the surface thereof, said particulate coating consisting essentially of a plurality of particles of an irregular shape similar to crushed stone and glacial stone, said particles passing through a 1 inch mesh and being retained on a inch mesh, each of the particles having a specific gravity of at least 0.9, said particles being a generally homogeneous synthetic resinous thermoplastic composiiton containing a light colored opaque filler, the thermoplastic resinous composition when molded requiring a force of up to 2 pounds to draw a rectangular face of molded composition, the face measuring 2.8 by 5 centimeters horizontally across a flat chromium plated surface, the molded composition being forced against the chromium plated face by a force of 4.2 pounds, the surface of the composition and the chromium plated surface being abraded uniformly by a 400 grit abrasive material to provide a plurality of generally parallel groovesin each of said surfaces, the surfaces being placed together in such a manner that the grooves in both surfaces are parallel and the force being exerted in the direction of the grooves.

2. The slope of claim 1, wherein said thermoplastic resinous composition is a polyolefin.

3. The ski slope of claim 1, wherein said filler is barytes.

41. The slope of claim 1, wherein said composition comprises an olefinic hydrocarbon polymer, wax, mineral oil and an inert inorganic tiller.

5. The slope of claim 4, wherein said thermoplastic resinous composition consists essentially of from about 10 to about percent of the total weight of the composition of an inert filler, from about 10 to 90 percent of a polyolefin polymer, up to percent of a wax and up to 20 percent of a mineral oil.

6. The slope of claim 5, wherein the thermoplastic resinous composition consists essentially of from 10 to about 70 percent polyolefin polymer up to about 20 percent of a paratfin wax, up to 10 percent mineral oil and from 30 to 70 percent of an inert inorganic filler.

7. The slope of claim 6, wherein said inorganic filler is barytes.

References Cited by the Examiner UNITED STATES PATENTS 2,339,958 1/1944 Sparks. 2,380,126 7/1945 Sturm 260738 2,558,759 7/1951 Johnson 260-285 3,066,580 12/1962 Alberti 94-3 3,091,998 6/1963 Wehr et al 94--3 OTHER REFERENCES Rose: Condensed Chemical Dictionary, sixth edition, Reinhold Publishing Corp, New York, p. 125, 1956.

MORRIS LIEBMAN, Primary Examiner.

D. C. KOLASCH, Examiner.

J. A. GAZEWOOD, Assistant Examiner. 

1. A SKI SLOPE HAVING A PARTICULATE COATING ON THE SURFACE THEREOF, SAID PARTICULATE COATING CONSISTING ESSENTIALLY OF A PLURALITY OF PARTICLES OF AN IRREGULAR SHAPE SIMILAR TO CRUSHED STONE AND GLACIAL STONE, SAID PARTICLES PASSING THROUGH A 1 INCH MESH AND BEING RETAINED ON A 3/8 INCH MESH, EACH OF THE PARTICLES HAVING A SPECIFIC GRAVITY OF AT LEAST 0.9, SAID PARTICLES BEING A GENERALLY HOMOGENEOUS SYNTHETIC RESINOUS THERMOPLASTIC COMPOSITION CONTAINING A LIGHT COLORED OPAQUE FILLER, THE THERMOPLASTIC RESINOUS COMPOSITION WHEN MOLDED REQUIRING A FORCE OF UP TO 2 POUNDS TO DRAW A RECTANGULAR FACE OF MOLDED COMPOSITION, THE FACE MEASURING 2.8 BY 5 CENTIMETERS HORIZONTALLY ACROSS A FLAT CHROMIUM PLATED SURFACE, THE MOLDED COMPOSITION BEING FORCED AGAINST THE CHROMIUM PLATED FACE BY A FORCE OF 4.2 POUNDS, THE SURFACE OF THE COMPOSITION AND THE CHROMIUM PLATED SURFACE BEING ABRADED UNIFORMLY BY A 400 GRIT ABRASIVE MATERIAL TO PROVIDE A PLURALITY OF GENERALLY PARALLEL GROOVES IN EACH OF SAID SURFACES, THE SURFACES BEING PLACED TOGETHER IN SUCH A MANNER THAT THE GROOVES, IN BOTH SURFACES ARE PARALLEL AND THE FORCE BEING EXERTED IN THE DIRECTION OF THE GROOVES. 